Unplug the external drive and plug it into a different USB port, ideally directly on the laptop rather than through a hub or dock. Try a different USB cable if the drive uses a separate one. Loose or hub-routed connections are the most common cause of drives not being detected.
Right-click Start > Device Manager, then look under 'DVD/CD-ROM drives'. If it's missing entirely, check under 'Other devices' or 'Universal Serial Bus controllers' for anything with a yellow warning triangle. If it's not listed anywhere, Windows isn't seeing the hardware at all, which points to a power, cable, or driver issue rather than the disc.